1. Field of the Invention
This invention relates to a process for preparing polyolefins by use of a novel polymerization catalyst. More particularly, it is concerned with a process for preparing polyolefins by polymerizing or copolymerizing olefins in the presence of a catalyst, said catalyst comprising a combination of a solid component which is obtained by copulverizing (1) a magnesium halide, (2) a compound represented by the general formula Al(OR)mX.sub.3-m wherein R is alkyl and/or aralkyl having 1 to 20 carbon atoms and may be the same or different, X is halogen and O&lt;m.ltoreq.3, (3) a tetravalent titanium compound and (4) a trivalent titanium compound, and a mixture which consists of (5) a trialkylaluminum and (6) an organoaluminum compound of the general formula AlR'nX.sub.3-n wherein R' is alkyl having 1 to 10 carbon atoms and may be the same or different, X is halogen and O&lt;n&lt;3, whereby the yield of polymer per solid and that per transition metal are remarkably increased resulting in the process dispensing with the step of removing residual catalyst in the polymer and at the same time the bulk density of the resulting polymer is hightened, the molecular weight distribution thereof is widened and consequently the fluidity of the polymer in a molten state is improved.
2. Description of the Prior Art
Heretofore, in the technical field of this sort, applicant of the present invention has found that if olefin polymerization is made by use of a catalyst which comprises a combination of a solid component obtained by copulverizing a magnesium halide, aluminum alkoxide and a tetravalent titanium compound, and an organoaluminum compound and/or an organozinc compound, the catalyst activity is remarkably increased and the resulting polymer has a high bulk density and an extremely improved impact strength (see Japanese patent public disclosure No. 64381/75). Also, applicant of the present invention has filed a patent application on his finding that a similar effect is obtained even by a combination of a solid component obtained by copulverizing a magnesium halide, an aluminum alkoxide and a trivalent titanium compound and/or vanadium compound, and an organoaluminum compound and/or an organozinc compound. However, all these prior inventions are disadvantageous in that the molecular weight distribution of the resulting polymer is narrow resulting in the fluidity of the polymer in a molten state being poor, although the polymer has a high impact strength.